1,721,246 research outputs found
Il paziente parzialmente edentulo candidato all’implantologia : valutazione della quantità ossea
No full textNANOSCALE MONITORING OF RESPONSIVE SUPRAMOLECULAR NANOSTRUCTURES AT THE SOLID-LIQUID INTERFACE
No full textThe self-assembly of small molecular modules into non-covalently linked polymeric nanostructures is a subject of continuous interest [1]. In particular, supramolecular structures with a high degree of order can be obtained through the self-association of organic molecules on flat solid surfaces. Such structures can be used as scaffolds to position electrically/optically active groups in pre-determined locations in 2D [2] thereby paving the way towards a wide range of applications, e.g. in electronic and optical devices. Among weak interactions, H-bonding offers high control over the process of molecular self-assembly because it combines reversibility, directionality, specificity and cooperativity. Such a unique character is the basis of sophisticated programs for self-assembly such as those based on the Watson–Crick base pairing which directs the formation of the helical structure of DNA.
While the self-assembly of guanines into G-quartet based architectures on solid surfaces has been studied by Scanning Tunneling Microscopy (STM) under ultrahigh vacuum (UHV) [3], STM explorations at the solid-liquid interface have been primarily carried out on guanosine derivatives [4]. In this lecture we will present a sub-molecularly resolved STM study at the solid-liquid interface of the metal templated reversible assembly/reassembly process of a N9-alkylguanine into highly ordered quartets and ribbons on highly oriented pyrolitic graphite (HOPG) surfaces. The self-assembly of guanine derivatives on HOPG has been studied as neat component[5] and upon sub-sequent addition of cryptand [2.2.2] molecules, potassium picrate and triflic acid to trigger the reversible interconversion between two different highly ordered supramolecular motifs, i.e. H-bonded ribbon and G-quartet based architectures. In-situ STM imaging provided the first direct evidence on the sub-nm scale of a dynamer operating at surfaces. [6]
Finally we will also provide the first example of sub-molecularly resolved vertically oriented switchable chromophores in physisorbed monolayers by monitoring the cis-trans isomerization of a physisorbed azobenzene at surfaces. [7]
The nanoscale visualization of such supramolecular interconversion at the solid-liquid interface opens new avenues towards understanding the mechanism of formation and functioning of complex architectures. Furthermore, the in-situ reversible assembly and re-assembly between two highly ordered supramolecular structures at a given surface represents the first step towards the generation of nanopatterned responsive architectures.
[1] J. M. Lehn, Science, 295, 2002, 2400.
[2] G. P. Spada, S. Lena, S. Masiero, S. Pieraccini, M. Surin, P. Samorì, Adv. Mater., 2008, 20, 2433; A. Ciesielski, L. Piot, P. Samorì, A. Jouaiti, M. W. Hosseini, Adv. Mater., 2009, 21, 1131.
[3] R. Otero, M. Schock, L. M. Molina, E. Laegsgaard, I. Stensgaard, B. Hammer, F. Besenbacher, Angew. Chem. Int. Ed., 2005, 44, 2270.
[4] G. Gottarelli, S. Masiero, E. Mezzina, S. Pieraccini, J. P. Rabe, P. Samorì, G. P. Spada, Chem. Eur. J., 2000, 6, 3242; T. Giorgi, S. Lena, P. Mariani, M. A. Cremonini, S. Masiero, S. Pieraccini, J. P. Rabe, P. Samorì, G. P. Spada, G. Gottarelli, J. Am. Chem. Soc., 2003, 125, 14741; S. Lena, G. Brancolini, G. Gottarelli, P. Mariani, S. Masiero, A. Venturini, V. Palermo, O. Pandoli, S. Pieraccini, P. Samorì, G. P. Spada, Chem. Eur. J., 2007, 13, 3757.
[5] A. Ciesielski, R. Perone, S. Pieraccini, G.P. Spada, P. Samorì, Chem. Commun 2010, 46, 4493.
[6] A. Ciesielski, S. Lena, S. Masiero, G. P. Spada, P. Samorì, Angew. Chem. Int. Ed. 2010, 49, 1963.
[7] D. Bléger, A. Ciesielski, P. Samorì, S. Hecht, 2010 submitted
The backstage of the ABC model: The Antirrhinum majus contribution
No full textAt the beginning of the 1990s, a simple genetic model that explained flower development was presented based on Arabidopsis thaliana and Antirrhinum majus floral homeotic mutants. According to this model, which is a milestone in plant development studies, flower development can be explained by three classes of genes (A, B and C), each one controlling the identity of organs in two adjacent whorls. Intriguingly, more than 20 years later, there are still some unanswered questions, in particular regarding the universality of the class A-function genes. Class A genes are well characterised in A. thaliana, but so far no A mutants have been described in other plant species nor in Antirrhinum majus. Here, we retrace the story that led to the proposal of the ABC model focusing on the contribution of A. majus to this model. Although fewer groups are still using A. majus as a model system, this plant was a master contributor to our comprehension of the molecular networks controlling flower developmen
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Due o tre cose che sappiamo di lei: una riflessione su "Rose" di Andre Dubus e Wanda di Barbara Loden
No full textTHE ROLE OF AUXIN DURING OVULE DEVELOPMENT IN ARABIDOPSIS
No full textAuxin is involved in many aspects of plant growth and development such as embryogenesis, organogenesis and vascular tissues differentiation. Auxin can trigger these moltitude of effects since it is polarly transported, and as a consequence specific spatial-temporal auxin gradients are created.
The Polar Auxin Transport (PAT) is due to the action of several auxin carriers: among them a major role is played by the 8 PIN proteins. PINs are polarly localized in the cell membrane, they can rapidly cycle inside the cell and a mutual regulation exists between PIN expression patterns and auxin concentration.
This research project focuses on the role of auxin during ovule development in Arabidopsis thaliana. We have introduced in Arabidopsis an artificial microRNA (amiRNA) directed against PIN1 that is under the control of an ovule specific promoter. Interestingly microscopic analysis show that in these transgenic plants ovule development is blocked at different stages of development. Preliminary results will be presented
- …
